CN107069768B - Hysteresis control strategy of STATCOM - Google Patents

Abstract

The application discloses a hysteresis control strategy of a STATCOM, which is characterized in that a target current i is calculated according to a measured voltage Uc of a capacitor bank and a target voltage Uref of the capacitor bank_sk ^*Amplitude A of (D); real-time acquisition of three-phase voltage V close to power supply end on alternating current side_abcWith three-phase current I_abcApplying the three-phase current I_abcAs a monitoring current i_sk(ii) a Will three-phase voltage V_abcObtaining a target current i through a phase-locked loop_sk ^*Phase angle theta of_abc(ii) a Target current i to be calculated_sk ^*Amplitude A and target current i_sk ^*Phase angle theta of_abcObtaining a target current i through sine_sk ^*(ii) a Target current i to be calculated_sk ^*With the collected monitoring current i_skCalculating a difference value; and sending the difference value to a hysteresis control module to obtain a trigger signal T for controlling the STATCOM. And the STATCOM sends out reactive current required by the load or absorbs the reactive current released by the load according to the trigger signal T. The application discloses, with the current of STATCOM alternating current side near power end as the control target, avoided traditional STATCOM control strategy to need the complex process of detecting reactive current, improve STATCOM's work efficiency, reduce the possibility of mistake.

Description

Hysteresis control strategy of STATCOM

Technical Field

The application relates to the technical field of power systems, in particular to a hysteresis control strategy of a STATCOM.

Background

A Static Synchronous Compensator (STATCOM) is a reactive power compensation device made of power electronics. Fig. 1 is an equivalent circuit diagram of a STATCOM, and as shown in fig. 1, the STATCOM is connected in parallel to a power grid or between the power grid and a load through a reactor. The basic components of a STATCOM include: a power switching device bridge and a capacitor bank. The power switching device bridge circuit comprises a plurality of switching tubes, and the switching tubes are controlled to be in an on-off state, so that the STATCOM reactive compensation is controlled to be started or stopped. In the context of figure 1 of the drawings,e_as,e_bs,e_cs,i_as,i_bs,i_csrespectively representing three-phase voltage and current supplied by the power supply, e_al,e_bl,e_cl,i_al,i_bl,i_clThree-phase voltage and current of load respectively.

When the load in the power grid is a pure resistive load, the voltage of the power grid is in phase with the current of the load, and at the moment, the load only consumes active power and does not consume reactive power, so that reactive compensation is not needed. When the load is an inductive or capacitive load, such as a transformer or a motor, the load consumes both real power and reactive power, and in this case, the grid or the reactive compensator is required to provide reactive power to the load, and this action of providing reactive power is reactive compensation. In a real grid, a grid or a reactive compensator is mostly required to provide reactive power for the grid or the reactive compensator.

The STATCOM is used as a compensation device for providing reactive power, and needs to send or absorb corresponding reactive power to a power grid according to the reactive power demand of a load, so that the reactive power only flows between the STATCOM and the load, and the power grid only transmits active power to the load.

The performance of a STATCOM depends on the method of obtaining the compensation current reference value and generating the compensation current control strategy. Currently, the control strategy of the STATCOM includes direct current control and indirect current control. The principle of the direct control of the STATCOM current is that the direct current control takes the voltage at the direct current side and the reactive current of a load as target values, and the dynamic reactive compensation of a power grid is realized by directly adjusting the output current of a power switching device bridge circuit. Therefore, in the direct current control, it is necessary to detect the reactive current.

The principle of the indirect control of the STATCOM current is that the reactive compensation purpose is achieved by adjusting the amplitude and the phase of the output voltage of the AC side of the bridge circuit of the power switching device. Among them, the target values of the amplitude and phase of the ac-side voltage are converted from the detected reactive current, and therefore, in the indirect current control, the reactive current needs to be detected.

In summary, it can be seen that, in both the direct current control method and the indirect current control method, a reactive component in the load current, i.e., a reactive current, needs to be detected. However, reactive current detection generally requires 5 times of matrix transformation to obtain reactive current, and multiple matrix transformation processes lead to complicated and complex reactive current detection processes and are prone to errors, thereby affecting the accuracy and the working efficiency of the STATCOM reactive compensation.

Disclosure of Invention

The application provides a hysteresis control strategy of a STATCOM, which aims to solve the problems that the existing STATCOM control strategy is complex in control process, high in matrix conversion times, high in number of used modules and prone to errors due to the fact that reactive current needs to be detected.

A hysteretic control strategy of a STATCOM comprises:

calculating a target current i according to the measured voltage Uc of the capacitor bank and the target voltage Uref of the capacitor bank_sk ^*Amplitude A of (D);

calculating a target current i according to the phase angle of the network voltage_sk ^*Phase angle theta of_abc；

According to the target current i_sk ^*Amplitude A and phase angle theta of_abcTo obtain a target current i_sk ^*；

Three-phase current I of collection STATCOM access circuit near power source end_abcAs a monitoring current i_sk；

According to the target current i_sk ^*And monitoring the current i_skAnd obtaining a trigger signal T for controlling the on-off of a switch tube in the STATCOM.

Preferably, said capacitor bank calculates a target current i based on a measured voltage Uc of the capacitor bank and a target voltage Uref of the capacitor bank_sk ^*The amplitude a of (a) may, in particular include,

measuring the measurement voltage Uc of the capacitor bank in real time;

calculating a difference value delta U between the measured voltage Uc of the capacitor bank and a target voltage Uref of a preset capacitor bank;

inputting the difference value delta U into a PI regulator to obtain a target current i_sk ^*The amplitude a of (a).

Preferably, the target current i is calculated from the phase angle of the grid voltage_sk ^*The phase angle of (a) may, in particular,

three-phase voltage V of acquisition electric wire netting_abc；

According to said three-phase voltage V_abcCalculating the three-phase voltage V_abcThe phase angle of (d);

according to three-phase voltage V_abcCalculating a target current i_sk ^*Phase angle theta of_abc。

Preferably, according to the target current i_sk ^*Amplitude A and phase angle theta of_abcTo obtain a target current i_sk ^*Specifically, the method comprises the following steps of,

a target current i_sk ^*Amplitude A and phase angle theta of_abcPerforming sinusoidal calculation to obtain a target current i for controlling measurement_sk ^*The waveform of (2).

Preferably, according to the target current i_sk ^*And monitoring the current i_skObtaining a trigger signal T for controlling the on-off of a switch tube in the STATCOM, which specifically comprises,

calculating a target current i_sk ^*And monitoring the current i_skThe hysteresis control module calculates a trigger signal T according to the current difference delta I, and the trigger signal T is used for controlling a switch tube in the STATCOM.

The application provides a hysteresis control strategy of STATCOM, takes the current of the alternating current side of the STATCOM close to the power supply end as a control target, avoids the complex process that the reactive current needs to be detected in the traditional STATCOM control strategy, improves the working efficiency of the STATCOM, and reduces the possibility of errors.

Drawings

In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without any creative effort.

FIG. 1 is an equivalent circuit diagram of a STATCOM;

FIG. 2 is a flowchart of an embodiment of a STATCOM hysteresis control strategy of the present application;

FIG. 3 shows the calculation of the target current i according to the present application_sk ^*A flow diagram of one embodiment of amplitude a;

FIG. 4 shows the calculation of the target current i according to the present application_sk ^*Phase angle theta of_abcA flow diagram of one embodiment of;

fig. 5 is a schematic diagram of an application of the STATCOM hysteresis control strategy to the power grid system according to the present application;

FIG. 6 is a waveform of grid voltage, grid current, load current and compensation current after application of a control strategy;

fig. 7 is a diagram of active and reactive waveforms after applying the control strategy.

Detailed Description

When the inductive load is connected with a power supply, the current phase of the inductive load lags behind the voltage phase of the inductive load; the capacitive load has the characteristic of preventing voltage abrupt change, and when the capacitive load is connected with a power supply, the current phase of the capacitive load is ahead of the voltage phase of the capacitive load, so that most power grids need reactive compensation.

The current of inductive or capacitive load is decomposed to obtain the active component and reactive component of current, i.e. I_l＝I_lq+I_ip. Wherein, I_lIs the load current; i is_lqIs the active component in the load current; i is_ipIs a reactive component in the inductive load current. The reactive compensation device is adopted to perform reactive compensation on the power grid system, and the aim is that the reactive compensation device provides all reactive current required by a load, and the power grid provides active current required by the load only to the load, even if the current output by the power grid to the load is I_lqIn the present application, the current is defined as the target current I of the power grid_sk ^*I.e. I_sk ^*＝I_lq。

The principle of the STATCOM hysteresis control strategy is that grid current before flowing into a load is monitored, the grid current is compared and analyzed with target current, the STATCOM is controlled to send reactive current required by the load to a grid system or absorb reactive current released by the load, output current of the grid is stabilized, and therefore fluctuation of the grid is reduced.

Fig. 2 is a flowchart of an embodiment of the hysteretic control strategy of the STATCOM of the present application, as shown in fig. 2, the hysteretic control strategy of the STATCOM comprises,

step S10, calculating a target current i according to the measured voltage Uc of the capacitor bank of the STATCOM and the target voltage Uref of the capacitor bank_sk ^*The amplitude a of (a).

FIG. 3 shows the calculation of the target current i according to the present application_sk ^*As shown in fig. 3, in the present embodiment, the target current i is calculated_sk ^*The process of the amplitude a of (a) specifically includes, step S11, measuring the measured voltage Uc of the capacitor bank of the STATCOM in real time; step S12, calculating a difference Δ U between the measured voltage Uc and a preset target voltage Uref; step S13, inputting the difference value delta U into a PI regulator to obtain a target current i_sk ^*The amplitude a of (a).

Difference value delta U and target current i_sk ^*A positive relation exists, namely when the difference value delta U is larger, the power grid is required to output a larger current; when the difference value delta U is smaller, the power grid is required to output a smaller current. In this embodiment, the target current i is calculated by inputting the difference value Δ U to the PI regulator and performing the PI tuning process_sk ^*The amplitude a of (a).

Step S20, calculating a target current i according to the phase angle of the grid voltage_sk ^*Phase angle theta of_abc。

FIG. 4 shows the calculation of the target current i according to the present application_sk ^*Phase angle theta of_abcAs shown in fig. 4, the flowchart of an embodiment of the present invention specifically includes, in step S21, acquiring the three-phase voltage V of the power grid in real time_abc(ii) a Step S22, according to the three-phase voltage V_abcCalculating the three-phase voltage V_abcThe phase angle of (d); step S23, according to three phasesVoltage V_abcCalculating a target current i_sk ^*Phase angle theta of_abc。

In the present application, a Phase Locked Loop (PLL) is used to obtain a target current i_sk ^*Phase angle theta of_abcSpecifically, the method comprises the steps of collecting the three-phase voltage V of the power grid in real time_abcAnd input to the PLL; PLL based on three-phase voltage V_abcCalculating a target current i_sk ^*Phase angle theta of_abc。

The calculation of the target current i will be described below by way of a specific example_sk ^*Phase angle theta_abcFirstly, the three-phase voltage V near the power supply end on the alternating current side of the STATCOM is collected in real time_abcWherein, A phase voltage V_aSin ω t, and a phase voltage of V_bSin (ω t +2 π/3), and a C-phase voltage of V_cSin (ω t +4 π/3). Then, the phase angle of each phase voltage is obtained from each phase voltage, and when t is 0, for example, the initial phase angle of each phase voltage is obtained, A, B, C phase voltages have initial phase angles of 0, 2 pi/3 and 4 pi/3, respectively. Of course, the phase angle at other times may be solved as well, and the control process after that is not affected. Finally, the obtained initial phase angles of the A, B, C phase voltages are respectively used as target currents i_sk ^*Phase angle theta of_abcI.e. the target current i_sk ^*The phase angle ratio of the A, B, C phase current is 0, 2 pi/3, and 4 pi/3.

Step S30, according to the target current i_sk ^*Amplitude A and phase angle theta of_abcTo obtain a target current i_sk ^*。

In the present embodiment, the target current i calculated in step S10 is used_sk ^*Is compared with the phase angle theta calculated in step S20_abcPerforming sine to obtain a target current i for controlling measurement_sk ^*The waveform of (2). The sine is a process of obtaining a standard current waveform according to the amplitude and the phase.

Step S40, collecting three-phase current I of the near power source end of the STATCOM access circuit_abcAs a monitoring current i_sk。

In the application, the STATCOM is connected to the three-phase current I of the near-power source end of the circuit_abcAs a monitoring current i_skNamely, the three-phase current I of the near-power source end of the STATCOM access circuit is monitored in real time_abcBy analysing the three-phase current I_abcAnd whether the reactive current exists in the load is known, so as to control the start or stop of the STATCOM reactive compensation operation, and the specific process is as described in step S50.

Step S50, according to the target current i_sk ^*And monitoring the current i_skAnd obtaining a trigger signal T for controlling the on-off of a switch tube in the STATCOM.

In the present application, the specific steps include calculating a target current i_sk ^*And monitoring the current i_skAnd the current difference value delta I is input to the hysteresis control module; the hysteresis control module calculates a trigger signal T according to the current difference value delta I, and the trigger signal T is used for controlling the on-off state of a switch tube in the STATCOM so as to control the on-off state of the reactive compensation work of the STATCOM. The hysteresis control module is used for calculating a relation value between the current difference value delta I and a preset threshold value, and then converting the relation value into an electrical trigger signal T.

Fig. 5 is a schematic diagram of an application of the STATCOM hysteresis control strategy to the power grid system, and as shown in fig. 5, the STATCOM is connected to the power grid, and the STATCOM selectively sends or absorbs reactive power to the power grid by controlling the on/off of a switching tube in the STATCOM, so as to implement reactive power compensation on the power grid.

In the actual control process, the measurement voltage Uc of the capacitor bank at the direct current side of the STATCOM is measured in real time, the difference value delta U between the measurement voltage Uc of the capacitor bank and the target voltage Uref of the capacitor bank is calculated, the difference value delta U is subjected to PI regulation, and the target current i is obtained_sk ^*Amplitude A of (D); meanwhile, the three-phase voltage V of the alternating current side near power supply end of the STATCOM is acquired in real time_abcWith three-phase current I_abcAnd applying the three-phase current I_abcAs a monitoring current i_sk(ii) a The obtained three-phase voltage V of the alternating current side close to the power supply end_abcThrough PLL, obtaining target current i_sk ^*Phase angle theta of_abc(ii) a Target current i to be calculated_sk ^*Amplitude A and target current i_sk ^*Phase angle theta of_abcObtaining a target current i through sine_sk ^*(ii) a Target current i to be calculated_sk ^*With the collected monitoring current i_skCalculating a difference value to obtain a current difference value delta I; and sending the current difference value delta I to a hysteresis control module to obtain a trigger signal T for controlling the on-off of a switch tube in the STATCOM. The trigger signal T controls the STATCOM to send reactive current needed by the load to the power grid or absorb reactive current released by the load.

Fig. 6 is a waveform diagram of the grid voltage, the grid current, the load current and the compensation current after the control strategy is applied, and as shown in fig. 6, the STATCOM is put into the system at 0.25s and cut off at 0.29 s. Within 0.25-0.29s, reactive current provided by the STATCOM is superposed with load current, and the superposed current and voltage have the same phase, so that the problem that the phase difference between the grid voltage and the grid current is increased due to the fact that a large amount of reactive power is consumed by the load is avoided, and the power factor of the grid is reduced.

Fig. 7 is an active and reactive waveform diagram after applying the control strategy, as shown in fig. 7, after the STATCOM is put into the power grid, the load current is in phase with the voltage of the power grid, the reactive power output by the power grid is reduced to zero, the output active power is kept unchanged, and the reactive power required by the load is completely sent out by the STATCOM, so that the reactive power compensation of the STATCOM on the power grid is realized.

The application provides a hysteresis control strategy of STATCOM, takes the current of the alternating current side of the STATCOM close to the power supply end as a control target, avoids the complex process that the reactive current needs to be detected in the traditional STATCOM control strategy, improves the working efficiency of the STATCOM, and reduces the possibility of errors. Meanwhile, in the aspect of working effect, the requirement of load reactive compensation can be well met under the conditions of fixed reactive compensation, dynamic switching and load jump, and the dynamic response speed is high and the precision is high.

The above-described embodiments of the present invention should not be construed as limiting the scope of the present invention.

Claims (3)

1. A hysteretic control strategy of a STATCOM, comprising:

calculating a target current i according to the measured voltage Uc of the capacitor bank and the target voltage Uref of the capacitor bank_sk ^*The amplitude a of (a) specifically includes measuring the measurement voltage Uc of the capacitor bank in real time; calculating a difference value delta U between the measured voltage Uc of the capacitor bank and a target voltage Uref of a preset capacitor bank; inputting the difference value delta U into a PI regulator to obtain the amplitude A of the target current;

calculating a target current i according to the phase angle of the network voltage_sk ^*Phase angle theta of_abc；

According to the target current i_sk ^*Amplitude A and phase angle theta of_abcTo obtain a target current i_sk ^*；

Three-phase current I of collection STATCOM access circuit near power source end_abcAs a monitoring current i_sk；

According to the target current i_sk ^*And monitoring the current i_skObtaining a trigger signal T for controlling the on-off of a switch tube in the STATCOM, specifically comprising calculating a target current i_sk ^*And monitoring the current i_skThe hysteresis control module calculates a trigger signal T according to the current difference delta I, and the trigger signal T is used for controlling a switch tube in the STATCOM.

2. The hysteretic control strategy of a STATCOM according to claim 1, characterized in that the target current i is calculated from the phase angle of the grid voltage_sk ^*The phase angle of (a) may, in particular,

three-phase voltage V of acquisition electric wire netting_abc；

According to said three-phase voltage V_abcCalculating the three-phase voltage V_abcThe phase angle of (d);

according to three-phase voltage V_abcCalculating a target current i_sk ^*Phase angle theta of_abc。

3. The hysteretic control strategy of a STATCOM of claim 1, wherein i is a function of a target current_sk ^*Amplitude A and phase angle theta of_abcTo obtain a target current i_sk ^*Specifically, the method comprises the following steps of,

a target current i_sk ^*Amplitude A and phase angle theta of_abcPerforming sinusoidal calculation to obtain a target current i for controlling measurement_sk ^*The waveform of (2).

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